Layered Division Multiplexing (LDM) .Layered Division Multiplexing • LDM super-imposes multiple

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  • Layered Division Multiplexing (LDM) Summary


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    Layered Division Multiplexing LDM super-imposes multiple physical layer data streams with

    different power levels, channel coding and modulation schemes for different services and reception environments;

    It enables more flexible use of spectrum to deliver mobile HDTV and UHDTV simultaneously in one 6 MHz channel to mobile, indoor, and fixed reception terminals;

    100% of RF bandwidth and 100% of the time are used to transmit the multi-layered signals for better time and frequency diversity, and robust reception;

    A receiver will decode the upper layer most robust signal first, cancel it from the received signal, and start decoding the second layer signal;

    LDM can have 3-6 SNR gain comparing with Traditional TDM system.

    LDM system: hierarchicalspectrum re-use to improve reception performance.

    RFChannel BW

    5 dB

    Stream A5 dB

    Stream B

    Stream C

  • LDM Tx Functional Architecture

    Framer Scrambler FEC1 Bit-Intl1 Mapper1 Time-IntlScheduler Freq IntlOFDM Framer / cell mux / TFS

    SFN IFFT GI Preamble/Spectrum Shaping


    Pilot / Tone Reserve


    Formatting BICM Freq Intl Preamble

    Data 1

    Control Info


    Output (SISO)


    Output (MIXO / TFS)

    FEC2 Bit-Intl2

    Data 2


    Injection Level

    Additional blocksRequired for LDM

    LDM is independent to MIMO, MISO, PLP, TI, Pilots, GI, pre-amble and PAR; LDM receiver complexity increase is less than 10%; LDM SNR performance gain is 4-6 dB for AWGN, and even higher SNR gains for mobile and strong multipath channels, due to stronger FEC and modulation used.


  • Cloud Txn Receiver (two layers) Diagram:


    A multi-layer system does not increase the receiver complexity by much; A large part of the circuits can be shared (tuner, sync, IF, ADC, AGC, equalizer, etc.); Upper layer needs FEC decoding, bit to symbol mapping, signal cancellation and

    DELAY data buffer; About 8% LDPC computation complexity increase and less than 10% memory

    increase for a 2-layer system receiver.

    Tuner IF & Down Converter

    Sync & Timing Clock Recovery

    A-D Converter OFDM Demod& Equalization


    Stream A


    Stream A Decoder

    Stream B Decoder Stream B

    + Bit to Cell Mapping

    Data + FEC

    Cell to LLR, LLR de-intl,LDPC decoder less than 10 iteration

    Data buffer:32k + cells

    Bit to cell mappingBit Intl 64kbits

    Time De-Intl

    Cell to LLR, LLR de-intlLDPC code less than 50 iterationCommon for TDM and LDM

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    LDM System (6 MHz RF Channel)


    Hierarchical spectrum re-use to improvespectrum efficiency and flexibility

    6 MHz RFChannel BW

    Injectionlevel 5 dB

    S/I = 5 dBI is lower layerinterference

    S/I = - 5 dBI is upper layerinterference

    Upper layer signal spectrum

    QPSKFEC R = 2.5 MbpsMobile HDTVS/N = - 3 dB

    Lower layer signal spectrum

    256QAMFEC R = 8/1524 MbpsUHDTV-4kS/N = 14 dB

    5 dBS/(N+I) = - 3 dBS/N = -1 dB

    Lower layerinterference

    C/I residual> 30 dB

    Lower layer signal afterUpper layer signal cancellation

    S/(N+I residual) S/N = 14 + 5 dB= 19 dBRef. to the total Tx power

    Direct decoding of upper layer signal

    Signal cancellationResidual/noise

    Two signals are super-imposed(symbol by symbol mix)at a selected injection level

  • More Flexible Use of Broadcasting spectrum In point-to-point communications, e.g., LTE, adaptive modulation and coding, as

    well as Tx power adaptation are used to fully explore the channel capacity; Broadcasting system is an one-to-many communication, the system is really

    designed to provide satisfactory service to the audiences at the End-of-Coverage; For audiences well inside the broadcast coverage area, they have very high field

    strength. This is not efficient use of channel capacity and those audiences can have better services;

    Solution: combine various services in one RF channel for tiered services.



    Field strength

    End of Coverage

    Traditional BroadcastingOne tier service


    Field strength

    Tier 1 Coverage

    Multi-layer services:Tier 1, 2 and 3

    Tier 3 CoverageTier 2 Coverage

    Tiered coverage is not new, ACATS proposals, DVB-T/T2, ISDB-T, ATSC M/H all can do it.LDM can make it working better, with more robust mobile/handheld HDTV solution.

  • LDM 2-Layer System Coverage (outdoor)with one robust mobile upper layer (S/N = 1.5 dB, 4 Mbps, 1080p/60 or 2 x 720p/60) and one high-data rate lower layer (S/N = +19 dB, 20 Mbps, 4k-UHD or multi-HDTV)

    Upper layer fix reception:10m directional antenna, F(50,90),S/N = 1.5 dB, 4 Mbps, 1080p/60Stationary HDTV, robust audio


    Lower layer fix reception:10m directional antenna,S/N = 19 dB, 20 Mbps, 4k-UHD or multiple HDTV 1080p,Immersive audio, F(50,90)

    Upper layer portable reception:1.5m Omni-directional antenna,S/N = 1.5 dB, 4 Mbps, 1080pPortable/handheld HDTV (tablets), Robust audio, F(50,90)

    Upper layer mobile reception: 1.5m Omni-directional antenna,S/N = 4.5 dB, 4 Mbps, 1080p HDTVVehicle speed (150+ km/h),Robust audio, F(90,90)

  • LDM Co-existence with other Technologies: A 2-layer LDM system, by nature, has one robust

    mobile/indoor PLP and one high data rate PLP for UHD or multiple HD services;

    LDM with layered transmission is naturally fit for Scalable Video Coding (SVC);

    Audio can be carried by robust mobile layer for extra-robustness;

    LDM can work with the traditional TDM/FDM to form 2-D or 3-D multiplexing;

    Backward compatible Future Extension Layer (FEL) can be added later, without impact the legacy services data rate.


  • LDM Flexibility: LDM is an enhanced TDM, which allows multi-layer

    transmission; A LDM system can do TDM, LDM, as well as mixed

    TDM/LDM; The injection level between layers is an important

    parameter to distribute the total transmitter power between layers;

    For example: A 6 dB injection level difference means 80% of the Tx power are assigned to mobile/indoor service, and 20% for fixed service;

    It gives broadcasters more flexibility!


  • Transition scenario and Future Extension Layer: During the transition period, an one-layer system can be

    deployed first to provide two 720p/60 HD mobile and indoor service at about 4 Mbps and SNR = -0.5 dB (AWGN);

    A lower layer can be added for 4k UHD or multiple HD fixed services, data rate ranges from 15 to 30 Mbps for high frame rate UHD at SNR = 14 to 24 dB;

    The two 720p/60 upper layer can be changed to one 1080p/60, if desired;

    Adding additional layers later without impact legacy services is one of the benefit on LDM: The legacy receiver will not go dark; the new service can be introduced seamlessly; CE can sell another round of new Rxs;

    The network is scalable and it can grow.


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    All SNR power levels are referenced to the total RF in-band power (of all layers)LDM: 16K FFT, GI= 1/16, P12,2. TDM: Fixed 32K FFT, GI = 1/32, P24,4; Mobile 8K FFT, GI = 1/8, P6,2.

    LDM vs. TDM SystemLDM (two layers) vs. DVB-T2+NGH (single layer, baseline code, no pre-amble)

    6 MHz RF Channel (-4 dB Lower Layer Injection)LDM System Mobile 55% Capacity Mobile 40% Capacity Mobile 30% Capacity


    Data rate SNR Data rate SNR Data rate SNR Data rate SNR

    2.0 MbpsQPSK 3/15

    -2.0 dB

    2.0 MbpsQPSK 6/15


    2.0 MbpsQPSK 8/15

    1.3 dB

    2.1 MbpsQPSK11/15


    Upper layer


    2.7 MbpsQPSK 4/15

    -0.3 dB

    2.7 MbpsQPSK 8/15

    1.3 dB

    2.7 MbpsQPSK 11/15


    2.6 Mbps16Q 7/15


    Upper layer


    4.1 MbpsQPSK 6/15

    2.7 dB

    4.1 Mbps16Q 6/15


    4.0 Mbps16Q 8/15


    4.1 Mbps16Q 11/15

    9.6 dB

    Low layer with -4 dB injection Fixed(TDM) 45% Fixed(TDM) 60% Fixed(TDM) 70%

    Low-rate 14.3 Mbps64Q 7/1514.6 dB

    14.4 Mbps256Q 11/15

    18.9 dB

    14.4 Mbps64Q 11/15

    14.4 dB

    15.3 Mbps64Q 10/15

    13.0 dB

    Mid-rate1 20.5 Mbps64Q 10/1518.5 dB

    19.6 Mbps1kQ 12/15

    25.6 dB

    21.0 Mbps256Q 12/15

    20.7 dB

    20.4 Mbps256Q 10/15

    17.3 dB

    Mid-rate2 24.6 Mbps256Q 9/1521.2 dB - N/A

    24.0 Mbps1kQ 11/15

    23.5 dB

    24.4 Mbps256Q 12/15

    20.7 dB

    High-rate 30.1 Mbps256Q 11/1524.4dB - N/A - N/A

    30.6 Mbps1kQ 12/15

    25.6 dB



  • LDM Prototype Hardware & Demo configuration


    Tx and Antenna(ch.50) Rx and An-


    HD (2.57Mbps, 60 fps,


    4k-UHD (19.43Mbps, 60 frames)

    Constella-tionController(Tx PC)


    Mobile/Indoor: 2.6 Mbps 720p SNR = -0.4dB. High data rate: 20Mbps 4kUHD SNR = 18.5 dB.

  • LDM Constellation on the Prototype Hardware14

    LDM Constellation Lower layer non-uniform 64QAM

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    Hardware Parameters @ 6MHz


    FFT Size 16K (16384)

    CP Size 1024 (6.25%)

    # of guard subcarriers 2751 (16.79%)

    # of used subcarriers 13633 (83.21%)

    # of pilot subcarriers 1197 (7.31%, PP2(12,2))Scattered/continual/edge pilots (from T2)

    # of data subcarriers 12436 (75.9%)

    OFDM sample length 7/48us (~0.1458 us)

    CP length 0.1493 ms

    Useful OFDM symbol length 2.3893 ms

    OFDM symbol length (Ts) 2.5387 ms